🔍 Key Concepts

• Thermostatic expansion valve (TXV) maintains correct superheat at the evaporator outlet • Superheat is the temperature of the refrigerant vapor above its saturation temperature at a given pressure • Effect of too much superheat on evaporator outlet condition and compressor suction line temperature

💭 Think About

• Think about what happens inside the evaporator if the TXV allows the refrigerant to be heated much more above saturation before leaving the coil—will there be more liquid or more vapor? • If almost all liquid is boiled off early in the evaporator, what will the remaining length of the coil and suction line be filled with—cold liquid/vapor mix or warmer superheated vapor? • Which of the options would you expect if there is LESS liquid available in the evaporator and MORE superheating of the remaining vapor?

✅ Before You Answer

• Recall that high superheat means very little or no liquid refrigerant at the evaporator outlet • Consider whether an overfed evaporator would cause high or low superheat • Ask yourself whether compressor suction line temperature would be colder or warmer if mostly superheated vapor (not liquid) is returning.